Potentiometer



Sept 1942- M. J. JOHNSON 2,297,187

POTENTIOMETER Filed May 9, 1939 4 Sheets-Sheet l INVENTOR Manfred J Lbhnson WWW ATTORNEYS P 1942- M. J. JOHNSON 2,297,187

POTENTIOMETER Filed May 9, 1959 4 Sheets-Sheet 2 INVEANTOR Manfred J Joimsrm ATTORNEYS p 29, 1942. M. J. JOHNSON 2,297,187

POTENTIOMETER Filed May 9, 19:59 4 Shets-Sheet 3 INVENTOR Manfred J Johnson ATTORNEYS Sept. 29, 1942.

M. J. JOHNSON 2,297,187

POTENTIOMETER Filed May 9, 1959 4 Sheets-Sheet 4 INVENTOR Y Marfred J John-$071 B fg,v ATTORNEY Patented Sept. 29. 1942 UNITED STATES PATENT OFFICE This invention relates to potentiometer systems, and, more particularly, to means for controlling the operation of the apparatus.

The problem that has been present in devices of this type is that of controlling the operating motor when a balanced condition exists. It was proposed to obtain this result by short-circuiting the input terminals of the motor or to providea balanced field which would tendto hold the motor in braked position and control its operation by oppositely wound field coils. In small motors of the fractional horsepower type, however,- the regulation is poor, and, therefore, but small braking effect is obtained by short-circuiting the input of the motor.

An object of the present invention is to provide the potentiometer in which the driving means is effectively braked immediately upon the balanced condition being reached or the control circuit for the balancing motor becoming inefiectlve to drive the motor. This is accomplished by the present invention by applying to the armature shaft of the motor which drives the slide wire contact a strong dynamic brake. This brake can either be in the form of a direct current winding on the pole piece to cooperate with the rotor of the motor, or it can be a separate field reacting on a separate armature carried by the motor shaft.

Inthe present preferred form of the invention,

the brake is normally applied to the motor to hold it against rotation and upon the control means for the motor being rendered operative to rotate the motorin either direction, the brake will be removed, and, upon the circuit becoming balanced and the control means rendered-inoperative, the brake will be immediately applied to plished by providing a means in the control circult for the motor for opening the circuit to the braking field upon the control means for the motor becoming operative. Also, the motor can be provided with a separate direct current fi'eld which, when energized, will oppose and neutralize I the direct current fieldthe energization being ferred form of the invention the braking field is the current ceasing to ilowin the control circuit,

the grid of the thermionic tube is returned to its normal potential and currentfagain flows in the braking circuit to apply a braking force to the rotor.

The braking of the motor can-also be accomcontrolled by the circuit controlling the operation of the motor to cause it to rotate in either direction.

If desired, the braking field can be contro led mechanically so that the braking circuit is opened during that period in which the drum contacts are in position to be engaged by the deflectable contact member of the galvanometer to cause the motor to run in either direction to balance the thermocouple circuit upon ofi-zero movement of the defiectable member. In this form of the invention, the brake is normally applied to the motor but is periodically removed.

The present invention, in its broader aspects, contemplates the application of a dynamic braking action to the motor of the balancing circuit so that the latter is'stopped immediately upon the balance being obtained; It will be seen, therefore, that a very accurate control will result inasmuch as it will avoid overrunning and reduce to a minimum'of time the balancing operation.

Other features and advantages will be apparent from the specification when considered in connection with the drawings, in-which:

Figure 1 shows a diagrammatic view of one form of the invention in which the brake is controlled through the thermionic tube.

Fig. 2 shows a diagrammatic view of the circuit in the form of the invention in which the direct current field is opened by a relay in accordance with the operation of the motor.

Fig. 3 is a diagrammatic view of the system in which an opposing D. C.v field is utilized to counteract the braking field when the motor is energized in either direction.

Fig. 4 is a diagrammatic view'of another form of the invention in which the'field' of the motor is energized with direct current to apply a. brake to the rotor and is adaptedito be connected to adapted to be connected to A. C. or D. C. current.

Fig. 7 shows the side view of the motor showing the separate pole piece for the braking field and a rotor on the armature shaft of the motor cooperating therewith.

Fig. 8 is a form of the invention in which the braking field is wound on the same pole piece as the energizing field.

Fig. 9 shows a form of the invention in which the braking field and opposing field are wound on the pole piece with the energizing field.

In the form of the invention shown in Fig. 1, the control system is similar to that shown in my Patent No. 2,109,776, wherein a galvanometer 2G or deflection instrument is provided with a the control circuit for energizing it for rotation in either direction becoming inefiective.

In the form of the invention shown in Fig. 1, a separate pole piece 551s secured to the frame of the motor and a separate rotor 56 preferably of the squirrel cage type isfsecured to the shaft of the motor so as to cooperate with the pole piece. A field 5? is wound on the pole piece and when energized with direct current it will, due to the generation of voltage in the rotating rotor, dynamically brake the same and hold it against rotation,

The D. C. current may be supplied to the braking field in many ways. In the forms of the inlong needle-like contact 2! which is periodically a thermocouple 28 or other source of voltage which is varied according to a change of condition. One side of the thermocouple is connected to the coil 21, while the other side is connected to a movable arm 30 having a contact 3! adapted to engage a slide wire 32 which is mounted on the periphery of a stationary disk 33. The other side of the slide wire is connected to a resistance 34 and a calibrating resistance 35, the latter having a movable contact 36 connected through a switch 31 to a source of current 38, which in turn is connected to the other end of the slide wire and to the galvanometer winding.

When the change in E. M. F. generated by the thermocouple occurs current flows through the galvanometer coil, the needle 2! will be defiected and the increase or decrease in potential is' counterbalanced by the adjustment of the slide wire.

The adjustment of the slide wire is accomplished in the illustrated form of the invention by use of a shaded-pole motor 39 having a constantly energized field db and oppositely wound shading coils M, "32 connected to the plates 43, M of a pair of thermionic devices or tubes 45, 36 through a transformer ll. The filaments 8, 59 of the tubes 45, 45, are energized from a winding 50 on a transformer 5| and the grids 52, 53 are connected through suitable resistors to be energized from winding 54 of the transformer, and are connected with the contacts 23, '24 on the drum in such a manner that, upon the needle engaging one of the contacts, it will change the potential on either grid 52, 53 and cause the current to'fiow in the corresponding pair of shading coils to operate the motor in the proper direction trolling thermionic tube 5% has its filament 59 connected across the transformer winding 5t supplying current to the filaments of the control tubes 55, 5S and its plate 66 connected to the D. C.iield.

The grid iii of the tube 58 is connected in the circuit so that it normally has the filament potential impressed thereon which causes a pulsating direct current to be impressed on the field coil from winding d2 of transfer 55. A condenser 63 shunted acims the lines smooths out the pulsating current.

The grid is also connected to the plate circuit of the tubes 55, 5$ through a drop resistor til, and a winding 65 on the transformer 5i. This connection is normally inoperative to control the grid, however, upon a change of voltage occurring in the thermocouple, the galvanometer needle will swing to right or left and engage either contact 23, 2d, changing the potential of the grid 52, 53 in the corresponding control tube d5, 65 to that value in which current will pass to the plate 33, 5 3 and energize the corresponding shading coils. This flow of current through the drop resistance will change the potential on the grid ti of the tube controlling the brake and will stop the now of current between the filament and the plate of this tube, and in efiect open the circuit to the direct current field.

This potential will remain on the grid iii of the brake control tube as long as current passes in the circuit controlling the rotation of the motor.

As soon as the motor has adjusted the slide wire so that a balanced condition exists in the thermocouple circuit and the galvanometer needle moves to zero position in which it no longer engages either contact on the drum, the grids of the control tubes will assume their normal potential and current will cease to fiow in the control circuit. Immediately upon the current ceasing to flow in the control circuit, the potential on the grid 5! of the brake control circuit will again assume the filament potential, and braking current will fiow to the braking field and quickly stop rotation of the motor.

Thus it will be seen that the braking action is immediately removed from the motor upon its energization to move it in either direction to balance the circuit, which braking action is restored as soon as the thermocouple circuit is balanced, thus efiectively preventing any overrunning of the motor.

In the form of the invention shown in Fig. 2, the control for balancing the circuit is the same as described in Fig. 1. In this form of the invention, the braking field 10 may be applied directly to the pole piece of the motor to coact with the rotor thereof, or can be applied as a separate pole piece and a rotor secured to the motor shaft to cooperate therewith,

The braking field is supplied with D. C. current from the power line through a transformer II and a rectifier I2. The braking field circuit has a normally closed switch I3 for completing the circuit so that the brake is normally applied to the motor. To open the circuit to the braking field at the switch, the present invention provides a relay 14 connected in the plate circuits .of the control tubes and operable, upon. current flow in the said plate circuits to cause the motor to rotate, to' release the brake.

Thus it will be seen that, upon a change of voltage being generated in the thermocouple, the needle will deflect to engage either contact on the drum, and will cause current to flow in the corresponding control tube plate circuit to load the shading coils to control the direction rotation of the motor. the plate circuit, the relay 14 will operate to open the switch I3 in the braking field circuit and remove the brake from the motor. As soon as the motor has moved the slide wire contact to that point in which the circuit is again balanced, the needle of the galvanometer will be in zero position and will stop the fiow of current in the control tube and deenergize the relay I4, whereupon the switch in the braking circuit will again close and apply the brake immediately without any overrunning of the motor.

In the form of the invention shown in Fig. 3, the control for the motor for balancing the circuit is similar to that shown in Fig. 1. In this form of the invention, a braking field 80 is either wound on the pole piece of the motor or on the separate pole piece to cooperate with a separate As soon as current flows in.

The switch is controlled by a relay}! in the plate circuit of the control tubes and operates to as the thermocouple generates a voltage to defleet the needle to engage either of the contacts 23, 24, the corresponding control tube is rendered conductive whereupon a current flows in the plate circuit to rotate the motor in the desired direction to balance the circuit. The current flowing in the plate will also flow in the opposing field circuit which will produce a field of such a magnitude as to oppose and neutralize the effect of the braking field, and thus permit the motor to run in the desired direction and adjust the slide wire.

As soon as the thermocouple circuit has been balanced, the needle of the galvanometer will again be brought to zero position, and the control tube rendered nonconductive. .This will remove the opposing field and permit the braking field to immediately stop the motor, thus preventing overrunning of the adjusting motor.

In the form of the invention shown in Fig. 4, the control circuit for balancing the thermocouple circuit is substantially the same as shown in Fig. 1. In this form of the invention, a main field winding 40 of the motor is connected to a switch 00. The switch normally connects the field to a source of D. C. current from the power lines, through a transformer 9| and a rectifier 92.

shift the field winding 00 from the source of a D. C. to a source of A. C. when it is desired to balance the circuit.

When current flows in the thermocouple circuit, the galvanometer needle will deflect to engage either contact. This will render the control tube associated with the contact operative to pass current to load the shading coils to rotate the motor in the desired direction. This will quickly operate the relay 94 to pull the switch over and connect the field to the source of A. C. current. The plate circuit of the control tubes, according to this form of the invention, receives its initial energization from a transformer winding 93 and immediately upon the operation of the switch the plate circuit will be also energized by the voltage generated in the shading coils.

As soon as the circuit is balanced, the galvanometer needle will return to zero position and the control tube again becomes nonconductive. This will immediately deenergize the relay 94, and the switch will again close the circuit to the field through the direct current supply, and brake the motor very quickly to prevent overrunning.

In the form of the invention shown in Fig. 5, the motor is controlled in a manner similar to that described in connection with Fig. l. The contacts 23', 24' on the drum in this form of the invention are provided with a straight cut-off line I00, and taper outwardly so that their forward edges IOI extend along the drum as shown. The contact 2| will always open the circuit at the same time, but can start the operation of the motor at diiierent times according to the amount of deflection. The motor is braked by a field I02 which is energized with direct current from the line through a transformer I03 and a rectifier I04. The energizing circuit for the brake includes a pair of normally closed contacts I05, I06, which are mechanically actuated and opened during that period of the revolution of the drum when the contacts are in a position to cooperate with the contact 2| to remove the braking action of the field. This is accomplished by providing a cam I01 which is secured to the shaft of the drum having a, cam face which will open the contacts for the duration of this period.

The cam will open the circuit to the braking field just prior to the contacts 23' and 24 moving into the zone in which they may engage the contact 2| so that the motor will be free to rotate in either direction upon the detection of an offzero movement so as to balance the circuit.

Thus it will be seen that the braking field circuit is not controlled by the control tubes for rotating the balancing motor but is mechanically opened, as by operation of the cam I01, for the period in each revolution of the drum during which the motor might be operated in either direction to balance the thermocouple circuit. It will be clear that once the motor has been braked and stopped, upon the closing of the contacts I05, I06, it is not necessary that the brake be applied continuously as the motor will not tend to rotate after it has once been brought to a stop.

Figs. 6 through 9 show various forms of motors for adjusting the slide wire to balance the thermocouple circuit. While it is to be understood any split phase motor or reversible A. C. motor may be utilized to drive the slide wire contact, the motors used for purpose of illustration are those in which oppositely wound shading coils control the direction of rotation of the motor.

In .the motor shown in Fig. 6, the main field coil 40 is of the type which can be connected to either A. C. or D. C. as shown in Fig. 4.

In the form of the invention shown in Fig. '1, the shaded pole motor is provided with a secondary pole piece 55 and a rotor 56 mounted on the armature shaft to cooperate therewith. -The secondary pole piece has a field coil 51 which is adapted to-be connected to the direct current source to hold the motor against rotation and have its circuit opened to permit the motor to be driven in either direction.

Fig. 8 shows the form of the invention in which the A. C. field winding lli'and D. C. field winding It are wound on the same pole piece. This type of motor, for example, can be used with the forms of the invention shown in Fig. 2.

Fig. 9 shows the normal A. C. field winding 68, and the two opposing D. C. field windings 88, 8d wound on the same pole piece. This type of motor can be used on the form of the invention shown in Fig. 3. I

Variations and modifications may be made within the scope of this invention and portions of th improvements may be used without others.

I claim:

1. In a potentiometer system, a slide wire;

means for unbalancing said system in accordance with a change in condition; a galvanometer controlled by said means and connected in circuit with the slide wire; means including analternating current motor having a continuously energized A. C. field, two wireewound shading coils and a D. C. field and including thermionic devices having their plate circuits energized by said shading coils and controlled by said galvanometer for adjusting the slide wire in accordance with the direction of off-zero movement of the galvanometer; means for energizing the D. C. field to hold the rotor of the motor against rotation; and means for deenergizing the D. C. field when the thermionic devices areoperative to actuate the motor to adjust the slide wire.

2. In a potentiometer system, a slide wire; means for unbalancing said system in accordance with a change in condition; a galvanometer controlled by saidmeans and connected in circuit with the slide wire; meansincluding an alterwith the extent or said off-zero movements; and a circuit including a direct current braking field and a thermionic relay normally supplying a current to said direct current braking field to hold the rotor aganist rotation, said relay being ren-' dered inoperative to supply the current to the braking field upon operation of the thermionic devices to load the shading coils to control the operation of the motor to balance the circuit.

4. In a potentiometer system, a slide wire; means for unbalancing said system in accordance 'with a change in condition; a galvanometer controlled by said means and connected in circuit with the slide wire; means including an alternating current motor having a continuously energized A. C. field and two sets of wire-wound shading coils and including thermionic devices having their plate circuits energized by the shading coils and controlled by the galvanometer for adjusting the slide wire directionally in accordance with ofi-zero movements of the galvanometer and quantitatively in accordance with the extent of said ofi-zero movements; a circuit including direct current braking field normally operative to hold the rotor against rotation; and a relay operable to alter the braking circuit upon operation of the thermionic devices to load the shading coils to control the operation of the motor to balance the circuit.

5. In a potentiometer system, an adjustable slide wire; means for unbalancing said system upon a change in condition; means for adjusting the slide wire to rebalance the system including a reversible motor; means for controlling the direction and extent of rotation of the motor in accordance with the variations and the magninating current motor having a rotor, a continu- 3. In a potentiometer system, a slide wire;

means for unbalancing said system in accordance with a change in condition; a galvanometer controlled by said means and connected in circuit with the-slide wire; means including an alternating current motor having a rotor, a continuously energized A. C. fie l d and two sets or wirewound shading coils and including thermionic devices having their plate circuits energized by the shading coils and controlled by the galvanometer for adjusting the slide wire directionally in accordance with ofi-zero movements of the galvanometer and quantitatively in accordance tude of the condition; a braking field normally applying a braking force to the rotor of the motor; and means for producing an opposing field Ior counterbalancing the braking field and rendering it inoperative upon the control means being rendered operative to cause the motor to rotate in either direction.

6. In a potentiometer system, a slide wire; means for unbalancing said system in accordance with a change in condition; a galvanometercontrolled by said means and connected in circuit with the slide wire; means including an alternating current motor having a continuously energized A. C. field and two sets of wire-wound shading coils and including thermionic devices having their plate circuits energized by the shading coils and controlled by the galvanometer for said .braking field upon operation of the ther! mionic devices to load the shading coils to-control the operation of the motor to balance the circuit.

7. In a potentiometer system, a slide wire; means for unbalancing said system in accordance with a change in condition; a galvanometer controlled by said means and connected in circuit with the slide wire; means including an alternating current motor having a continuously energized A. C. field, two wire-wound shading coils and two oppositely wound D. C. fields, and thermionic devices having their plate circuits energized by said shading coils and controlled by said galvanometer for adjusting the slide wire in accordance with the direction of off-zero movement of the galvanometer; means for continuously energizing one of the D. C. fields to electrically lock the rotor against rotation; and means for energizing the other D. C. field to oppose and counterbalance the first D. C. field upon the thermionic devices being rendered operative to load the shading coils to adjust the slide wire to balance the system.

8'. In a potentiometer system, an adjustable slide wire; means for unbalancing said system upon a change in condition; means for adjusting the slide wire-to rebalance the system including a reversible motor having a braking field thereon; means for controlling the direction and extent of rotation of the motor in accordance with a variation and magnitude of the condition; means for normally applying direct current to the braking field to dynamically brake the motor and hold it against rotation; and means for cutting oi! the supply of direct current to the braking field when the control means is in operative relation to rotate the motor in either direction.

9. In a potentiometer system, an adjustable slide wire; means for unbalancing said system the braking field to dynamically brake the motor a variation and magnitude of the condition; means for normally applying direct current to and hold it against rotation; and mechanically operated means for opening the circuit to the braking field when the means for controlling the direction and extent of rotation of the motor is in position to be efiective to control said motor.

10. In a potentiometer system, a slide wire; means for unbalancing said system upon a change in condition; an adjusting motor connected to said slide wire to move it to balance said system; a galvanometer to rebalance the system connected in the circuit of the slide wire and having a defiectable member; a rotatable drum having contacts thereon to cooperate with the defiectable member to control the direction and extent of rotation of the adjusting motor in accordance with the variation and magnitude of the condition; a braking field for the motor; means for normally applying a direct current to the braking field to hold the motor against rotation; and means operating in timed relation with the drum for opening the circuit to the braking field during the period when the contacts on the drum are in position to cooperate with the defiectable member to cause the motor to rotate in either direction.

MANFRED J JOHNSON, 

